Considering the currently measured mass of the secondary star in HD 259440 (15.7\(\pm \) 2.5 M\(_{\odot }\) , [1]} [1]}) and the timescales associated to the encounter with Stock 10, it is likely that at least 40% of its current mass was gained during initial mass transfer. This would also imply that the primary star was stripped from 6.2 M\(_{\odot }\)  off of its ZAMS mass of 12.7 M\(_{\odot }\)  While no pulse period was detected in HD 259440, the stellar masses at play largely favor the presence of a neutron star in this HMXB.
